Cyanogenic Glycosides and the fate of cyanide in soil

Cyanogenic glycosides are a group of nitrile-contanining, plant secondary compounds that yields cyanide (cyanogenesis) following their enzymatic breakdown. Although there are many natural sources of cyanide, including the plants, bacteria and fungi that synthesize and secrete it, the most significant sources of cyanide in the environment are industrial wastes. Soil as a weathered system does not contain cyanides nor does it generate cyanides, except indirectly in supporting the growth of microorganisms, plants and other intimate soil life and of course through anthropogenic activities. The loading rate in soil is the paramount factor determining toxicity to microorganisms or hazard for movement into groundwater and food chain. Cyanide played a primary role in the evolution of life on earth and remains an important form of nitrogen for microorganisms, fungi and plants. The co-evolution between plants, herbivores and pathogens may have afforded some insects and fungi the ability to overcome the defense system based on cyanogenic glycosides, either by their ability to transform the compounds into non-toxic constituents or by sequestration and further use in their own defense. Mobility of cyanide in soils is mostly influenced by volatilization and distribution. However, the rate of volatilization from soils is complex and depends on many factors. The author now reviews the above mentioned factors and with some emphasis on the biological elimination of cyanide.